1. Field of the Invention
The present invention relates to rotary kilns and, more specifically, to rotary kilns which employ a drum which rotates on at least one shaft. The shaft, in turn, rotates on at least one bearing which automatically axially aligns itself with the longitudinal axis of the shaft.
2. Background Information
Rotary kilns are well known in the art. One particular type of rotary kiln employs an elongated, cylindrical drum that is rotatably supported such that the longitudinal axis of the drum is inclined with respect to the horizontal. Material, to be processed by the kiln, enters the elevated end of the rotating drum while a hot gas, such as air, is blown into the lower end of the rotating drum. As the drum rotates, gravity pulls the material downward, through the drum, while the rising hot gas, moving in the opposite direction of the material, heats the material. The rotation of the drum mixes, or stirs the material and ensures that the hot gas throughly mixes and often reacts with all or a substantial part of the material. The processed material then exits the lower end of the drum.
The drum is rotated on at least one shaft and the shaft is rotated on a at least one bearing. Typically, at least four shafts are employed with each shaft rotating on two bearings. The typical bearing usually includes two bearing surfaces, which are orthogonal to one another, so that the bearing can accept loading in two series of directions; one parallel to the longitudinal axis of the shaft and one orthogonal to the longitudinal axis of the shaft. Under ideal conditions the shaft and the bearing are aligned, with one another, so that the load of the drum and shaft is evenly distributed on the bearing surfaces.
However, several factors can contribute to partial misalignment between the shaft and the bearing surfaces, thereby causing the load of the drum and the shaft to be unevenly supported by the bearing. That, in turn, may cause the bearing surfaces to wear excessively in areas where they are most heavily loaded. Such excessive wear may cause premature failure of the bearing. Factors that may cause uneven loading of the bearing surfaces include uneven weight distribution of the material in the drum, or freezing and thawing of the ground on which the kiln is constructed or settling of piers. Such uneven loading may cause the shaft to become misaligned with the bearing. Also, the drum may even twist due to some warping, possibly because of uneven distribution of hot gas that is blown through the drum.
A need, therefore, exists for a bearing for a rotary kiln, that can automatically align the liner surfaces of the bearing with the shaft, or shafts, of the kiln, even when the rotary drum is unevenly loaded, or when the drum distorts or warps.
Several patents exist which are directed to rotary kilns. U.S. Pat. No. 4,129,036 discloses an alignment indicator for a roller-type support. The device disclosed in this patent provides an indication of the alignment of the bearing and does not automatically compensate for bearing misalignment.
U.S. Pat. No. 4,171,949 discloses an arrangement for supporting a rotary drum such as a rotary kiln. The device disclosed in this patent employs carrying beams which provides mechanical equalization of the forces exerted on a roller of the kiln during rotation of the drum.
U.S. Pat. No. 4,500,285 discloses a rotary kiln with a kiln cylinder that has an annular bearing ring for supporting the kiln. Spacer plates are located between a ring and an outer surface of the cylinder. This patent is not directed to automatically compensating for bearing misalignment.
U.S. Pat. No. 4,511,266 discloses a rotary kiln that is supported on an annular bearing ring having an inner circumference that is larger than the outer circumference of the kiln cylinder. This patent is not directed to automatically compensating bearing misalignment.
Patents relating to bearings include U.S. Pat. No. 4,129,343, which discloses a self-aligning bearing. This patent is not directed to rotary kilns. Further, the bearing disclosed in this patent does not include two orthogonal bearing surfaces that, each, self-align due to bearing misalignment.
U.S. Pat. No. 4,288,128 discloses a self-aligning thrust bearing. This patent, also, is not directed to rotary kilns. Further, the bearing disclosed in this patent does not include two orthogonal bearing surfaces that, each, self-align due to bearing misalignment.
U.S. Pat. No. 4,586,664 discloses a bearing support system for a cone crusher. The device disclosed in this patent is not directed to rotary kilns and does not provide any self-alignment whatsoever.
Rocker seat type bearings, as a trunnion bearings, have been employed in grinding mills. Also, pivoted pad thrust bearings have been employed as part of a radial, multi-pad journal bearing for large grinding mills. Further, water cooling of bearings has been employed in mill trunnion bearings. However, none of these applications employs a device that is similar to the claimed invention.